The need for articles produced from nonwoven containing nanofibers has continued to increase. So has the need for additional functional particulates in the articles comprising nonwoven webs. The nanofibers webs are desired due to their high surface area, low pore size, and other characteristics. The nanofibers, also commonly called microfibers or very fine fibers, typically range in diameters of less than 1000 nanometer or one micron. The nanofibers can be produced by a variety of methods and from a variety of materials.
The risk with dispersing particulates in the nonwoven webs is the falling out of particulates during handling or use. Particulate retention in the web is improved with finer fibers. Therefore, it is desirable to use nanofibers in the nonwoven web to contain the particulates. Although several methods have been used to make nanofiber nonwoven webs, there are drawbacks to each of the methods and producing cost effective nanofibers has been difficult. Therefore, hygiene articles and other disposable consumer products containing nanofibers with or without functional particulates have not been marketed.
Methods of producing nanofibers include melt blowing, melt film fibrillation, film fibrillation, electro-spinning, and solution spinning. Other methods of producing nanofibers includes spinning a larger diameter bicomponent fiber in an islands-in-the-sea, segmented pie, or other configuration where the fiber is then further processed so that nanofibers result.
Melt blowing is a commonly used method of producing fine fibers and webs containing such fibers and additional particulates. The latter is generally referred to as “coforming”. Examples of coforming particulates with fine fibers has been given by U.S. Pat. Nos. 4,100,324; 4,784,892; and 4,818,464 assigned to Kimberly-Clark Corp. Typical melt-blown fiber diameters range from 1.5 to 10 microns, for example, as utilized in the above methods. Though particulates are mechanically held captive by the fibers, there is a limitation of particulate size to prevent loss of particulates during handling. Therefore, it is desirable to use nanofibers to allow effective containment of finer particulates in the nonwoven web.
Melt blowing can be used to make fibers with smaller diameters, such as nanofibers, but with considerable changes needed to the process. Commonly, redesigned nozzles and dies are needed. Examples of these include U.S. Pat. Nos. 5,679,379 and 6,114,017 by Fabbricante et al. and U.S. Pat. Nos. 5,260,003 and 5,114,631 by Nyssen et al. and U.S. patent application Ser. No. 2002/0117782 by Haynes et al. These methods utilize relatively high pressures, temperatures, and velocities to achieve the small fiber diameter. The above-mentioned methods have not been used to make webs with nanofibers and particulates.
Attempts have been made to minimize loss of particulates from the fine fiber webs. An example of one such method includes U.S. Pat. No. 6,494,974 by Riddell assigned to Kimberly-Clark Worldwide. There the reduction in loss of particulates is achieved by heating the particulates to a temperature near that of melt-blown fibers and then impacting the stream of heated particulates onto the melt-blown fibers such that particulates penetrate the fiber surface and get embedded. Disadvantage of such method is that the particulates have to be heat-stable and extra energy to heat the particulates is needed.
Other methods of incorporating particulates in nonwoven webs are air-laying and spunbonding. These methods utilize relatively large diameter fibers to make nonwoven webs, typically greater than 10 micron fiber diameter.
It is an object of the present invention to provide webs containing nanofibers and particulates. It is also an object of the invention to produce low cost nanofibers web containing particulates. It is also an object of the present invention to provide a method of forming a web from melt film fibrillation comprising particulates and fibers.